This invention relates generally to imaging systems using pixilated detectors, and more particularly to pixilated semiconductor detectors in imaging systems.
Imaging devices, such as gamma cameras and computed tomography (CT) imaging systems, are used in the medical field to detect radioactive emission events emanating from a subject, such as a patient and to detect transmission x-rays attenuated by the subject, respectively. An output, typically in the form of an image that graphically illustrates the distribution of the sources of the emissions within the object and/or the distribution of attenuation of the object is formed from these detections. An imaging device may have one or more detectors that detect the number of emissions, for example, gamma rays in the range of 140 keV, and may have one or more detectors to detect x-rays that have passed through the object. Each of the detected emissions and x-rays is typically referred to as a “count,” but may also be counted together as a ‘signal current’ and the detector determines the number of counts received at different spatial positions. The imager then uses the count tallies to determine the distribution of the gamma sources and x-ray attenuator, typically in the form of a graphical image having different colors or shadings that represent the processed count tallies.
A pixilated semiconductor detector, for example, a detector fabricated from cadmium zinc telluride (CZT), may provide an economical method of detecting the gamma rays and x-rays. However, a low energy tail on the energy spectrum resulting from the CZT interaction with the radiation may interfere with the ability to distinguish direct gamma rays and x-rays from scattered gamma rays and x-rays. The tail may result from a different response of the semiconductor material in the regions between the pixels compared to the response from within the pixels.
Another problem that may be associated with using a pixilated semiconductor detector is a loss of potential detector spatial resolution due to a gap between a detector collimator and the active detector surface. The gap is a result of known mounting technology that makes collimator exchange easier. The divergence of the gamma and x-ray photons in the gap may contribute to a degradation of a spatial resolution realizable from the detector. At least some known imaging devices use a variety of interchangeable collimators for respective different applications. Each collimator may differ in length and bore of the holes, and the weight of the collimators necessitates special handling equipment and procedures. This further increases the likelihood of a degradation of spatial resolution of the detector.
Furthermore, due to the fine tolerances needed to achieve accurate resolution of detector images, producing collimators having holes that are substantially aligned with each detector pixel is difficult, thus affecting image resolution.